Porsche 914-4 Weber Carb running rich, Weber Carb running rich on #4 only Options

[mturner7]

Hi Everyone,

My car is a 1974, 914-4 with a 2.0L (2056cc) engine. With Weber IDF 44's.
My #4 cylinder is running really rich. All the others are fine.

The Question is: What in the carburetor could most likely cause the plug to foul (Running very rich) like in my case? I've tried to adj the air/fuel mixture screw still no change.

This is what I've done so far:

0) Did a compression check on all cylinders. All ok. (95-100psi) 
1) Changed the plugs.
2) Changed the Cap and Rotor.
3) Changed the plug wires.
4) Verified all the jets are the same.
5) Set the Air flow on each carb, sync'd them
6) I cleaned all the jets with the carb in the car, ran and idled much better.
7) Verified Spark to that Cyl, got a hell of a shock out of it.
8) I'm running Elec-Ignition, Flamethrower Coil, 60,000volts.

After doing all this, the #4 plug still fouls after only about 20 to 30 miles. It has to be the carburetor.

I just pulled the carburetor. Thanks for the help.

[Superhawk996]

Those carbs have been modified

1st thing I would suspect is blockage within the thin brass tubes that lead to the calibrated brass bushings that supply air to the idle jet

IDF’s run on the idle circuit when cruising under light load.

I would also measure all the jets and make sure someone hasn’t drilled out #4 larger than what it is stamped as.

[Tbrown4x4]

Also look at how the throttle plate uncovers the progression holes. If the plates are bent or damaged, or the shaft and plates have been replaced, fuel can be drawn into the cylinder when it shouldn’t be.

If there is an enrichment circuit under the cover, make sure it’s not allowing fuel past when it’s not supposed to.

[dr914@autoatlanta.com]

all good advice, additionally 44s are too large for a 914 engine which will accentuate any problem

[930cabman]

all good advice, additionally 44s are too large for a 914 engine which will accentuate any problem

(IMG:style_emoticons/default/agree.gif) (IMG:style_emoticons/default/agree.gif)

For fun I tried 44's on my 2056 and no way. I switched to 40's and never looked back. She runs great, pulls nicely, idles great and gets a bit over 30MPG cruising at 75 MPH

[infraredcalvin]

Not much to add to the above, but have you moved idles/mains, etc around, see it the issues follows?

Also is this a newly developed issue when previously ran fine?

[mturner7]

Those carbs have been modified

1st thing I would suspect is blockage within the thin brass tubes that lead to the calibrated brass bushings that supply air to the idle jet

IDF’s run on the idle circuit when cruising under light load.

I would also measure all the jets and make sure someone hasn’t drilled out #4 larger than what it is stamped as.

Hi, the thin brass tubes that lead to the calibrated brass bushings that supply air to the idle jet were not clogged.

All the jet are the same, because I replaced them with new ones during the troubleshooting process a while back.

Main = 1.35
A/C = 2.00
Idle = 55
jet in the bottom of the bowl = 55
Venturi's = 32 (i'm going to put in the 36's)
Secondary Venturi's = 4.5
pump jet = 50

Carb is dirty, but haven't found the smoking gun.

[mturner7]

Not much to add to the above, but have you moved idles/mains, etc around, see it the issues follows?

Also is this a newly developed issue when previously ran fine?

Hey Calvin,

This problem came with the car. When i took a look at the main jets for the car, the previous owner had bigger jets for #4 & #3. (1.60's drilled out to about 1.80) & bigger A/C jets on #4 also. He had 1.60's in #1 & #2. It was running kind of rough so i looked at the plugs and #4 was fouled.

I purchased all new jets and installed 1.35 mains all around and stock A/C's (2.00).

Current config:
Main = 1.35
A/C = 2.00
Idle = 55
jet in the bottom of the bowl = 55
Venturi's = 32 (i'm going to put in the 36's)
Secondary Venturi's = 4.5
pump jet = 50

Once I installed the current conf above, new plugs, cleaned the idle jets, sync'd the carbs, it ran way better and smother. It wasn't cutting out at low rpms anymore and it was idling great. I could also start out in second gear now! After i purchased new plug wires, cap & rotor, I adjusted the valves. They were all ok, no adjustment necessary. But after all that and driving it for a while it will start popping. I pull the plugs and #4 is always fouled.

I did notice a small lost in power on the freeway after down jetting it.

Well I just cleaned #3 & #4 carbs. Replaced everything that came in the kit.
I also put back in the 36 Venturis. I'm going to pull the other carb and do the same.

Monte

[930cabman]

If anything I would go with 28mm venturis, not 36's

[Dave_Darling]

Have you checked the valve adjustment? Double-checked the ignition timing? Checked for vacuum leaks?

--DD

[technicalninja]

If anything I would go with 28mm venturis, not 36's

(IMG:style_emoticons/default/agree.gif)

Do they make 28mm vents for the 44 IDF?

Smallest I've found is 32s for the 44IDFs

Mturner7, the reason the mains were so large was the previous owner tried to add more fuel to a carb size up that was poorly matched to the engine it was on.

The real problem was too little vacuum at the booster.

You put the basic stock jets back in it and now you do not have enough fuel in the upper end.

That carb should be on a 2.2l or bigger street motor.

It would work on a 2.0l competition engine. I would expect a power band from 4-8K only.
Below 4k it would be a dog...

You need a higher vacuum signal. These are the only ways I know how to do that.
Increase engine size or RPM range (increase airflow).
Decrease butterfly and venturi size. I think you're already on the smallest vents available for your 44s.

Some carburetors have special auxiliary venturis that are "dog legged" deeper in the main venturi.
Some have annular boosters. Makes TBI style spray from the boosters.
Don't think either of those are available for the IDF series.

Bottom line, carbs are too big for a street based 2 liter...

The funkiness with cylinder #4 may be something different but having badly matched carb to engine size would make diagnosis far more difficult to do.

The change back to the proper size mains is probably running the engine way lean (your loss of power) and may be running it way too hot.

A WB02 sensor and a good CHT gauge should be part of any serious tuning IMO.
Extended use above 400 degrees will hurt the metallurgy of the air-cooled heads.
It looks damn easy to hit this number with a slightly improper tune.
I would guess yours is WAY off...

[rhodyguy]

The one air bypass screw looks to be way way open.

[Superhawk996]

Also look at how the throttle plate uncovers the progression holes. If the plates are bent or damaged, or the shaft and plates have been replaced, fuel can be drawn into the cylinder when it shouldn’t be.

If there is an enrichment circuit under the cover, make sure it’s not allowing fuel past when it’s not supposed to.

Given the other easy things that appear to have been ruled out.

(IMG:style_emoticons/default/agree.gif)

A twisted throttle shaft could account for why #4 is richer than #3.

I’m assuming there is no enrichment circuit there based on the cover and lack of lever arm to actuate the little valves but it’s worth verifying.

[rfinegan]

After basics are set up for valve lash, timing, float level etc
tune like a new set of carbs...
1) Fresh plugs
2) Deactivate the accelerator pumps
3) PULL the main jet stacks
4) Adjust you idle circuit (best lean)
5) Test drive..
6) Check plugs for rich
Follow up with tuning the transition circuit /test drive for rich
Follow up with main jet tuning/test drive for rich
Adjust accelerator pump / test for rich

Lets see where you are running rich...

[SirAndy]

If anything I would go with 28mm venturis, not 36's

(IMG:style_emoticons/default/agree.gif)

The smaller, the better since the 44s are already too big for that engine.

[Spoke]

Hijack (again):

On my 2056, I have some popping when the engine is pre-warm. No popping after warmed up.

Carb settings:

Weber IDF 40
28mm venturis,
115 mains
Idle Jets: 50
airjets 200
F11 emulsion tube

Recently adjusted valves (didn't change anything)
No vacuum leaks.
No info on cam or valves. (2L heads)

Adjusted the idle vacuum for each side and idle bypass screws were all about 1 1/2 turns out. Engine ran pretty good.

Then about a week ago, it started running very rough, like on 3 cylinders when at idle and light throttle. With heavy throttle, it pulled like crazy.

Seemed like #2 was not firing. On cold start up and just idling with some revving, I checked the temps of the exhaust pipes and #2 pipe was cold. Pulled the plug wire while running (using an insulated hose pliers) and the engine slowed down a bit so the plug was firing.

Sprayed carb cleaner on all the intake interfaces and no change in engine tune so likely no obvious vacuum leaks.

I backed out the idle screw many turns and the engine smoothed out at idle. Took it for a ride and it ran ok; not great; just ok. Exhaust tubes were all similar heat so #2 was firing ok.

I'm going to pull the carb and inspect. What should I be looking for?

[technicalninja]

The 115 mains are the only thing that jumps out at me. 130/135 is more common.

Are you running a WB02?

Are you running a CHT?

What are your readings if you are?

I'd expect 15/1 and HOT from those jets

All of the jets except the mains are original sizes IMO.

Commonly a main jetting change of that magnitude will also require an air correction jet change as well.
The ONLY air correction jets I've seen have all been 200.
I own 3 sets of IDFs now. A pair of 40s and two pair of 44.
One 44 set has 170 mains in it now. Someone was trying to "cheat" around having too big a carburetor with this pair.

Get a WB02 if you don't have one.

Takes most of the guessing out of the equation.

I am gathering jets for tuning now. This is what I'm starting with.

Mains 125/130/135/140.
Airs 180,190,200,210
Idles 45/50/52/55

One thing I've noticed with the used carbs I've purchased is multiple jets are missing their sealing O-rings. These WILL NOT work without the correct O-rings.
If your O-rings are more than 5 years old, they should be replaced. I'd use HBNR AC O-rings in a pinch, but I have thousands of these so it's easy for me.

I'd pull the idles and clean them out for your drivability issue first.

First 30-40% of operation is on these jets, and they are tiny.

[Superhawk996]

I'm going to pull the carb and inspect. What should I be looking for?

@spoke

No need to remove the carbs yet.



Pull idle jets - clean and blow out with air
Edit: CRITICAL - limit air pressure to about 2-3 psi - ie very gentle. With fuel still in the bowl - blowing air though the idle passages will pick up some fuel out of the bowl - short bursts - not extended blowing though the passages - we are only clearing minor debris or corrosion particles. And should go without saying don’t do this in the presence of sparks or flames!

Blow air though the idle air correction bushing (non removable brass bushing at top)

Blow air through the idle jet hole.

Remove idle mixture screw(s) - clean; inspect. Often you will find some rust or corrosion on the needle. Clean up with steel wool or 3m scrubbie.

If you find heavy corrosion on a needle it may need to be replaced but not usually. Likewise, if there is heavy corrosion on a needle, spray carb clean into the hole to help break up any corrosion in the idle port then blow again with compressed air.

Blow air though the mix screw hole to clear the idle port and transition ports of any debris or corrosion.

Reinstall everything; set idle mix; resynch carbs

All this can be done in car without need to remove carbs and linkages.

[technicalninja]

https://www.piercemanifolds.com/CHOKE_p/71507.htm


Pierce lists 28 venturis for the 44IDF.

This should solve most of the "too big" in this application.

[Spoke]

I'm going to pull the carb and inspect. What should I be looking for?

@spoke

No need to remove the carbs yet.



Pull idle jets - clean and blow out with air
Edit: CRITICAL - limit air pressure to about 2-3 psi - ie very gentle. With fuel still in the bowl - blowing air though the idle passages will pick up some fuel out of the bowl - short bursts - not extended blowing though the passages - we are only clearing minor debris or corrosion particles. And should go without saying don’t do this in the presence of sparks or flames!

Blow air though the idle air correction bushing (non removable brass bushing at top)

Blow air through the idle jet hole.

Remove idle mixture screw(s) - clean; inspect. Often you will find some rust or corrosion on the needle. Clean up with steel wool or 3m scrubbie.

If you find heavy corrosion on a needle it may need to be replaced but not usually. Likewise, if there is heavy corrosion on a needle, spray carb clean into the hole to help break up any corrosion in the idle port then blow again with compressed air.

Blow air though the mix screw hole to clear the idle port and transition ports of any debris or corrosion.

Reinstall everything; set idle mix; resynch carbs

All this can be done in car without need to remove carbs and linkages.

@Superhawk996

Thanks for the tips. About the idle jets, are they where this picture has the vacuum hose? I'm not well versed in carbs but I did stay at a Holiday Inn Express sometime in my past.